Aim: Exercise training elicits diverse effects on brown (BAT) and white adipose tissue (WAT) physiology in rodents housed below their thermoneutral zone (i.e., 28-32 • C). In these conditions, BAT is chronically hyperactive and, unlike human residence, closer to thermoneutrality. Therefore, we set out to determine the effects of exercise training in obese animals at 28 • C (i.e., thermoneutrality) on BAT and WAT in its basal (i.e., inactive) state. Methods: Sprague-Dawley rats (n = 12) were housed at thermoneutrality from 3 weeks of age and fed a high-fat diet. At 12 weeks of age half these animals were randomized to 4-weeks of swim-training (1 h/day, 5 days per week). Following a metabolic assessment interscapular and perivascular BAT and inguinal (I)WAT were taken for analysis of thermogenic genes and the proteome. Results: Exercise attenuated weight gain but did not affect total fat mass or thermogenic gene expression. Proteomics revealed an impact of exercise training on 2-oxoglutarate metabolic process, mitochondrial respiratory chain complex IV, carbon metabolism, and oxidative phosphorylation. This was accompanied by an upregulation of multiple proteins involved in skeletal muscle physiology in BAT and an upregulation of muscle specific markers (i.e., Myod1, CkM, Mb, and MyoG). UCP1 mRNA was undetectable in IWAT with proteomics highlighting changes to DNA binding, the positive regulation of apoptosis, HIF-1 signaling and cytokine-cytokine receptor interaction. Conclusion: Exercise training reduced weight gain in obese animals at thermoneutrality and is accompanied by an oxidative signature in BAT which is accompanied by a muscle-like signature rather than induction of thermogenic genes. This may represent a new, UCP1-independent pathway through which BAT physiology is regulated by exercise training.

Background and aimExercise training elicits diverse effects on brown (BAT) and white adipose tissue (WAT) physiology in rodents. However, these animals are typically housed below their thermoneutral zone (i.e. 28-32°C). In these conditions, BAT is chronically hyperactive and, unlike human residence, closer to thermoneutrality. Therefore, we set out to determine the effects of exercise training in obese animals at 28°C (i.e. thermoneutrality) on BAT and WAT in its basal (i.e. inactive) state.MethodsSprague-Dawley rats (n=12) were housed at thermoneutrality from 3 weeks of age and fed a high-fat diet (HFD). At 12 weeks of age half these animals were randomised to 4-weeks of exercise exercise training, i.e. swim-training (1 hour/day, 5 days per week). Metabolic assessment was undertaken during the final 48h and was followed by interscapular and perivascular BAT and inguinal (I)WAT sampling for the analysis of thermogenic genes and the proteome.ResultsExercise attenuated weight gain but did not affect fat mass or general metabolic parameters (i.e. fasting insulin and glucose). Interestingly, although BAT mass was increased, there was no change in thermogenic gene expression. Differentially regulated proteins in BAT enriched gene ontology (GO) terms including 2-oxoglutarate metabolic process, cytochrome-c activity and mitochondrial respiratory chain complex IV. This was accompanied by an upregulation of multiple proteins and GO terms involved in skeletal muscle physiology suggesting an adipocyte to myocyte switch in BAT. UCP1 mRNA was undetectable in IWAT despite an increase in classical ‘browning’ markers (i.e. PGC1a and ADRB3) with exercise. Enriched GO terms in IWAT included DNA binding and positive regulation of apoptosis. Impact analysis highlighted carbon metabolism and OXPHOS pathways were regulated by exercise in BAT whilst HIF-1 signalling and cytokine-cytokine receptor interaction were among those modified in IWAT.ConclusionExercise training reduces weight gain in obese animals at thermoneutrality and is accompanied by an oxidative, myogenic signature in BAT, rather than induction of thermogenic genes. This may represent a new, UCP1-independent pathway through which BAT regulates body weight at thermoneutrality.

Background and aim:Rodents are commonly housed below thermoneutrality and this exposure to 'cold' (i.e. 20°C) activates thermogenic brown (BAT) and beiging of white adipose tissue. Here, we examined whether a standard housing temperature (i.e. 20°C, a reduction in temperature of ~8°C) or YM-178, a highly-selective β 3-adrenoreceptor agonist, in obese animals raised at thermoneutrality, would impact differently on classical BAT or subcutaneous inguinal (IWAT) beige depots. Methods: Eighteen weanling Sprague-Dawley rats were housed at thermoneutrality (28°C) and fed a high-fat diet. At 12 weeks, 6 animals were randomised to either standard housing temperature (20°C, n=6) or to β 3-AR agonist administration (28°C+β3, 0.75mg/kg/d, n=6) for 4 weeks. Metabolic assessment was undertaken during the final 48h, followed by interscapular, perivascular BAT and IWAT sampling for the analysis of thermogenic genes and the proteome. Results: Exposure to 20°C increased weight gain, BAT and IWAT mass. Proteomic analysis of BAT revealed novel pathways associated with cold-induced weight gain (i.e. histone deacetylation, glycosaminoglycan degradation and glycosphingolipid biosynthesis) whilst β 3adrenoreceptor agonism impacted on proteins involved in skeletal muscle contraction and cell differentiation. IWAT of cold-exposed animals exhibited an enrichment of proteins involved NAD+ binding, plus retinol and tyrosine metabolic pathways whilst β 3-AR agonism downregulated ribosomal and upregulated acute phase response proteins. Conclusion: Following diet-induced obesity at thermoneutrality, exposure to 20°C promotes subcutaneous fat deposition in order to reduce heat loss and defend body temperature. In contrast, chronic administration of β 3-AR agonist has minimal metabolic-related effects on adipose tissue.

Therapeutic activation of thermogenic brown adipose tissue (BAT) may be feasible to prevent, or treat, cardiometabolic disease. However, rodents are commonly housed below thermoneutrality (~20 °C) which can modulate their metabolism and physiology including the hyperactivation of brown (BAT) and beige white adipose tissue. We housed animals at thermoneutrality from weaning to chronically supress BAT, mimic human physiology and explore the efficacy of chronic, mild cold exposure (20 °C) and β3-adrenoreceptor agonism (YM-178) under these conditions. Using metabolic phenotyping and exploratory proteomics we show that transfer from 28 °C to 20 °C drives weight gain and a 125% increase in subcutaneous fat mass, an effect not seen with YM-178 administration, thus suggesting a direct effect of a cool ambient temperature in promoting weight gain and further adiposity in obese rats. Following chronic suppression of BAT, uncoupling protein 1 mRNA was undetectable in the subcutaneous inguinal white adipose tissue (IWAT) in all groups. Using exploratory adipose tissue proteomics, we reveal novel gene ontology terms associated with cold-induced weight gain in BAT and IWAT whilst Reactome pathway analysis highlights the regulation of mitotic (i.e., G2/M transition) and metabolism of amino acids and derivatives pathways. Conversely, YM-178 had minimal metabolic-related effects but modified pathways involved in proteolysis (i.e., eukaryotic translation initiation) and RNA surveillance across both tissues. Taken together these findings are indicative of a novel mechanism whereby animals increase body weight and fat mass following chronic suppression of adaptive thermogenesis from weaning. In addition, treatment with a B3-adrenoreceptor agonist did not improve metabolic health in obese animals raised at thermoneutrality.